Conventional map information display devices which display a present position of a displacement body on a map are known in the navigation systems or the like of automobiles. FIG. 1 is a block diagram of a conventional map information display device such as disclosed in non-examined Japanese utility model publication JP-U-3-10278. FIG. 2 is an explanatory diagram showing a display example displayed on a display section.
In FIG. 1, reference numeral 1 denotes a CD-ROM (compact disk . read on memory) in which map data is stored, 2 is an operational section into which commands are input by a user, 3 is a bearing sensor of the displacement body, 4 is a displacement amount sensor, 5 is a bearing calculation means. 6 is a processing device which performs overall control of the map information display device. 7 is a system controller, 8 is a map data buffer memory. 9 is a display device acting as a display section, 10 is a CRT (cathode ray tube) controller, 11 is a first VRAM (image random access memory), 12 is a second VRAM, 13 is a read controller, 14 is a CRT.
The processing device 6 generates images so that the present position of the displacement body is in the center and stores such images in the first VRAM. The image reading region (window) is displaced and scrolled in the first VRAM 11 depending on the displacement of the displacement body. The window is monitored to ascertain whether the map reading region has reached a preset region or not. When the preset region is reached, the generated image is stored in the second VRAM so that the present position of the displacement body is at a center. Thereafter the window in the second VRAM 12 displaces by scrolling depending on the displacement of the displacement body. Thereafter the process is repeated whereby images are generated, recorded and scroll displayed together with the displacement of the displacement body each time a region in which a window is preset in each VRAM 11, 12 is reached.
The recording region of the first VRAM 11 (the same as the second VRAM 12) is present in simplified form in FIG. 2. As shown in the figure, a rear plotting initial line (hereafter back drawing line) is provided in a region which is smaller on all sides than the first VRAM 11. A window WD1 is provided in a region which is again smaller on all sides. The center CAR1 of the window WD1 corresponds to the present position of the displacement body.
The operation of the invention will be described below.
FIG. 3 is a flowchart showing the flow of map drawing processing in such a map information display device. The process device 6 reads map data corresponding to the present position of the displacement body from the CD-ROM and inputs the read data into the CRT controller 10 of the display device 9. The CRT controller 10 generates an image so that the present position of the displacement is in the center and records the image in the first VRAM 11 (step ST1). Next a VRAM (first VRAM 11) which reads the image from the read controller 13 is designated and a position of the window WD1 of the first VRAM 11 is determined so that the cursor which shows the position of displacement of the displacement body is expressed in the center of the screen.
The read controller 13 reads a map image from the window WD1 of the position determined for the designated first VRAM 11 and displays it on the CRT 14 (step ST3). Monitoring is performed to check whether the window WD1 has reached the back drawing line BDL1 or not. If the line has not been reached, the routine returns to step ST2 and the process after the calculation of the window address of the window WD1 which depends on the displacement of the displacement body is repeated (step ST4). In this way, the position of the window WD1 which depends on the displacement of the displacement body is moved and the map image is displayed by scrolling.
If the displacement body has traversed a considerable distance, the window WD1 reaches the back draw line BDL1, the process device 6 reads map data which depends on the present position of the displacement body from the CD-ROM 1 and inputs the data into the CRT controller 10 of the display device 19. The CRT controller 10 generates an image so that the present position of the displacement body is in the center and stores the image in the second VRAM 12 (step ST5). Next a position of the window WD2 of the second VRAM 12 is determined so that the cursor which shows the present position of the displacement body is in the center of the screen and that address is input into the read controller 13 (step ST6).
The read controller 13 reads the map image from the window WD2 at a determined position for the designated second VRAM 12 and expresses the map in the CRT 14 (step ST7). Monitoring is performed to check whether the window WD2 has reached the back drawing line BDL2 or not. If the line has not been reached, the routine returns to step ST6 and the process after the calculation of the window address of the window WD2 which depends on the displacement of the displacement body is repeated (step ST8). In this way, the position of the window WD2 which depends on the displacement of the displacement body is moved and the map image is displayed by scrolling.
If the displacement body has traversed a considerable distance, the window WD2 reaches the back draw line BDL2, the routine returns to step ST1 and repeats the process after the storing of the map image in the first VRAM 11.
Apart from the above noted technique related to a conventional map information display device, published patent applications JP-A-7-218279 and JP-A-7-286857 are also noted.
Since the conventional map information display device is constructed as above, the icon (present position mark) which shows the present position of the displacement body is in the center of the display. Normally from the point of view of the driver who is driving the displacement body, information about the proximity of the displacement body is required when the displacement body is travelling at low speeds and information further forward is required at high speeds. It is advantageous to have information about areas forward of the displacement body at a wider range a high speeds than at low speeds. However in the conventional map information display device, the icon which displays the present position of the displacement body is displayed in the center and the driver can thus obtain map information regarding the environs of the present position. Thus the problem has arisen that it is difficult to display a map screen as desired by the driver.
The present invention is proposed to solve the above problems and has the object of providing a map information display device with a front extended display by which a driver can obtain information at a wider range at high speeds than at low speeds.